I know a lot of people that pitch right on top of the previous yeast cake with no problems. Just make sure that you are brewing a simular color and style when doing so. There will be some of your previous batch in there. Also, smell the yeast to ensure that there are no off flavors detected. Do not wait too long. If you are going to transfer and than brew the following Weekend, store the yeast in the refrig and make a starter with it. JMTC

Who will tell you that there will be a lot of trub in the bottom of your fermentor that is not healthy and will lead to off flavors. There is a process called washing the yeast were you add boiled and cooled water to the cake, agitate it, let it sit for a few minutes for the crap to settle. Pour off your yeast water to be used as a yeast starter. If you keep your process sanitary and your yeast happy, they can be used over and over. If you notice under performance, it's time for new yeast.

I recently did the same thing. I timed the racking of the finished beer to coincide with the cooled off new batch, racked the finished beer into a keg, then transfered the newly brewed and cooled wort right in the same primary on top of the yeast. I shook up and roused the yeast and then aeriated, then put her away to do it's thing. I checked back on it 2.5 hours later and fermentation was is full gear!

I would only consider racking directly on the previous yeast only once, as to me after that it may harm your beer with off flavors from excess trub. Why take that chance? But you can always capture some of the yeast to cultivate for future sessions.

I too am considering the yeast re-pitching but I will have a lag time between batches of about 2 weeks.

Couple of questions:

1. How much should I capture from my primary to re-use?

2. Say I make a 3 qt starter with this yeast and split into several pint containers, will they keep in the fridge for me to brew 6 batches? By my schedule above, approximately 3 months? (given I would make a starter with the stored yeast prior to pitching)

3. Any pointers for the yeast washing? What's worked best, etc...

I make a lot of IPAs (or at least I try to) so re-using WL001 would be perfect. Any way I can reduce my per batch brewing costs, the more the wife will give the go ahead to brew.

It has been said that if handled correctly and stored in a cold fridge, harvest yeast should be used within 2 weeks of harvest. I haven't tried going any longer than that, but when I want to re-pitch yeast, I try to time it so that on brew day, I rack the finished beer from the primary...then rack the cooled off wort from my session right on top of the yeast in the primary. This really works good for me and hardly any lag time.

As far as storing, I would think that the 2 week window should be observed. I have never kept yeast beyond that length of time, but would like to hear from others that may have kept it longer and what their results were.

You can capture as much of it as you can safely store I would imagine. Some wash their yeast before reusing and others don't. Try to get at least a nice big slug of it, and make sure to make a starter before reusing to make sure it is viable.

When you buy a vial or smack pack, it is older than two weeks. Why would you think that the yeast off the primary would have a shorter life?
I will give you that special care has to be taken to ensure that you are putting viable yeast into hibernation. I call it the wash 'em, feed 'em and put them to bed program.
1. Separate them from the majority of the trub as described above.
2. Make a fresh starter
3. Put them in the refrigerator before fermentation of the starter is complete.
I have had success for 3-4 months following these steps.
I you are concerned that it may be too long, bring them out and feed 'em and put them back to bed.

yes....the yeast will last longer than 2 weeks, and i don't remember ever stating that the yeast would perish after that time. I should have stated that for maximum viability, it has been said that you should try to use your harvested in 2 weeks, and if not, ensure that they are stored appropriately in a cold environment.

I have used white lab yeasts with success being way past the due date on the vial. Way past it....for instance....i just used a vile of dusseldorf alt yeast last Nov that was 6 months past the use before date. I did make a starter to prove the yeast out...and it was fine. My LHBS actually gives his yeast that's past the due date to me either for half price or for free, depending on what mood he's in at the time. Either way its a win situation for me!

When I harvest the yeast I swirl enough to get the top ~2/3 of the yeast cake into suspension, assuiming that the bottom 1/3-1/2 should contain most of the break material. I figure that the trub carried over is only a fraction of that in the new batch, so I don't wash my yeast. I don't feel that much is gained by washing unless you use something like Chlorine Dioxide, but that's really just my opinion.

I calculated once that somewhere around 1.5 cups or a pint of my yeast cake should give me an appropriate pitch rate for a ~1.050 beer. I like to let the yeast grow a little for each fermentation, so I don't use a whole cake, but that also reduces the amount of trub that's carried over.

I've read that harvested yeast cake viability drops to about 80% after 2 weeks and 50% after 1 month when stored in the fridge. I try to use harvested yeast within 2 weeks, at which time I pitch directly from the fridge. If I use it later, I usually create a starter. I give myself an arbitrary discard date of about 6 weeks. I get rapid starts within 2 weeks, but they can become noticeably slower after that.